Magnetizing fixture with insulated core

ABSTRACT

A magnetizing fixture is provided for connection to an electrical power supply. Electrically conductive elements fit within channels connecting top and bottom surfaces of an electrically conductive core. One end of each electrically conductive element connects to a power supply and the other end to an electrically conductive top. An electrically insulating layer coating the channels and top and bottom surfaces of the electrically conductive core electrically isolates the electrically conductive elements from the electrically conductive core.

PRIORITY

This application is a divisional application of U.S. patent applicationSer. No. 10/666,525, filed Sep. 18, 2003, now U.S. Pat. No. 7,061,353and which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a magnetizing fixture, and moreparticularly, to a magnetizing fixture of motor magnets.

BACKGROUND ART

Magnets are employed in a variety of appliances where the applicationoften dictates the physical shape of the magnet and the pattern ofmagnetization. For example, the rotor of a DC motor incorporates amagnet in the shape of a hollow cylinder where the magnetization isgenerally radial, that is, perpendicular to the cylindrical walls.Although it is possible to construct various magnet shapes from severalstandard sized and shaped magnets, it is often preferable to achieve thedesired magnetization with a single object having the desired shape.

During magnetization, an object to be permanently magnetized is placedin a region having a magnetic field with a particular configuration. Tothat end, such a magnetic field often is generated with a magnetizingsystem. One type of magnetizing system includes a magnetizer thatsupplies electrical current to a coupled magnetizing fixture. Thefixture typically has an electrically conductive, non-permanentlymagnetizeable core of substantial magnetic permeablilty to concentrateand focus the magnetic fields produced by current flowing through aplurality of surrounding conductors. To begin magnetization,magnetizeable material to be permanently magnetized, e.g., steel, may beplaced around or about the magnetizing fixture. The magnetizing systemthen generates a magnetic field to magnetize the material.

Proper configuration of the magnetic fields requires that electricalcurrent flow only through the electrical conductors. Undesirably,because of contact between the conductors and the core, current often isdiverted into the steel core. Current flowing through the core thusdistorts both the resulting magnetic fields and, consequently, thesubsequent permanent magnetization of the object being magnetized.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a magnetizing fixture isprovided for connection to an electrical power supply. The magnetizingfixture has an electrically conductive structure with an electricallyconductive top and several electrically conductive elements, the firstends connected to a power supply and the second ends to the electricallyconductive top. An electrically conductive core of substantial magneticpermeability has a top surface coupled to the electrically conductivetop and channels communicating from the top surface to the bottomsurface of the core. Each electrically conductive element is containedin a channel. The top and bottom surfaces of the electrically conductivecore and the channels are coated with an electrically insulating layer.

In accordance with an embodiment of the invention, the channels may beopen and may completely contain the electrically conductive elementslaterally.

In accordance with an additional embodiment of the invention, theinsulating layer may contain several sublayers. In an embodiment wherethe insulating layer contains two sublayers, the first sublayer maycontain nickel, chromium, and yttrium and the second may containstabilized zirconia.

In accordance with a further embodiment of the invention, adjacentelectrically conductive elements may be connected to differentelectrical connections.

In accordance with another aspect of the invention, a method is providedfor constructing a magnetizing fixture. An electrically conductivestructure that forms an interior and an electrically conductive core ofsubstantial magnetic permeability are provided. After coating a part ofthe electrically conductive core with an electrically insulatingmaterial, the insulated core is secured within the interior of theconductive structure. Securing may be done by soldering the conductivestructure to another structure, where the melting temperature of theelectrically insulating material exceeds the soldering temperature.

In accordance with a further embodiment of the invention, channels maybe formed in the electrically conductive core between a top and a bottomsurface and the channels and top and bottom surfaces may be coated withthe electrically insulating material. The electrically insulatingmaterial may include a first layer of nickel, chromium, aluminum, andyttrium, and a second layer of stabilized zirconia.

In accordance with a further aspect of the invention, a magnetizingfixture is provided with an electrically conductive element capable ofreceiving power from a power source, an electrically conductive core ofsubstantial magnetic permeability positioned within the conductiveelement, and an insulator that prevents electrical contact between atleast a portion of the conductive element and the conductive core.

In accordance with still another embodiment of the invention, aninsulator may coat the conductive core.

In accordance with a still further embodiment of the invention, theconductive element may include legs electrically connected with a powersource terminal. Each leg may have a first end and a second end, wherethe second ends of the legs may be connected together and each first endmay be connected to a positive or negative power source terminal.

In accordance with a still additional embodiment of the invention, aconnection material may connect a bar connected to a power supply portwith the conductive element. The connection material may have a meltingpoint less than the melting point of the insulator. The connectionmaterial may be a solder and, in certain embodiments, may be a silversolder.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention will be more readily understoodby reference to the following detailed description, taken with referenceto the accompanying drawings, in which:

FIG. 1 shows an illustrative magnetizing system that can incorporatevarious embodiments of the invention.

FIG. 2 shows schematically an embodiment of a magnetizing fixture.

FIG. 3A is a schematic top view, FIG. 3B a schematic front view, FIG. 3Ca schematic side view, and FIG. 3D a schematic cross-sectional view ofthe magnetizing fixture shown in FIG. 2.

FIG. 4A shows schematically an embodiment of an electrically conductivestructure as incorporated in the magnetizing fixture shown in FIG. 2.FIG. 4B is a schematic side view and FIG. 4C a schematic top view of theelectrically conductive structure.

FIG. 5A shows schematically an embodiment of electrical connections asincorporated in the magnetizing fixture shown in FIG. 2. FIG. 5B andFIG. 5C are schematic top and front views respectively of the electricalconnection. FIG. 5D and FIG. 5E are schematic front and sidecross-sectional views respectively of the electrical connection.

FIG. 6A shows schematically an electrically conductive core ofsubstantial magnetic permeability. FIG. 6B is a schematic top view ofthe core. FIG. 6C and FIG. 6D are schematic front and sidecross-sectional views respectively of the core.

FIG. 7 shows a process for making an embodiment of the magnetizingfixture.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Magnets are central to the operation of many motor-driven appliances. Inthe case of ordinary DC or brushless DC electric fans, rotating magneticfields created by sequential excitation of electrical currents in statorwindings interact with magnets located on a rotor to provide torque torotate the rotor in a desired manner. The magnetic field established bythe stator is designed to interact with the magnetic field establishedby the rotor magnets. For example, in single phase excitation, if therotor contains six magnetic poles of particular angular width anddistribution, the stator has a similar number and arrangement ofmagnetic poles. In the case of three phase excitation, there may be nineor more poles.

It is advantageous to construct the rotor magnet by magnetizing a singleobject of magnetizable material rather than from assembly of individualmagnets. Among other reasons, assembly is simpler and more accurate.However, the advantages depend on the reliable magnetization of therotor magnet.

Magnetization takes place when the object to be magnetized is positionedin the vicinity of magnetic fields that are consistent with the geometryof the object and the required magnetization pattern. For a cylindricalrotor magnet, the desired magnetization is radial in direction (i.e.,through the thickness of the magnet) with equal numbers of north andsouth poles.

Magnetic fields generated by electrical currents flowing throughconductors lack the focus required for effective magnetization of theobject. Placement of conductors near suitably shaped magnetic materialof substantial magnetic permeability may properly concentrate magneticfields if no air gaps are present between the conductors and the shapedmagnetic material. A magnetic material, such as cold rolled steel,possessing a magnetic permeability relative to the magnetic permeabilityfree space of more than about 100 has substantial magnetic permeability.To preserve electrical isolation in the absence of physical isolation,various embodiments of the invention provide an electrically insulatingmaterial to separate the conductors and the shaped magnetic material.

FIG. 1 shows a magnetizing system 100 that may incorporate illustrativeembodiments of the invention. The magnetizing system includes amagnetizer 110 that applies electrical current to an attachedmagnetizing fixture 120. In illustrative embodiments, a magnetizableobject 130 is slipped over the outer surface 125 of fixture 120. Oncethe object 130 is in place, the magnetizer 110 delivers current to thefixture 120, thus producing a magnetic field. This magnetic fieldconsequently permanently magnetizes the magnetizable object 130. Detailsof the interaction between the magnetizer 110 and the magnetizingfixture 120 are discussed below.

FIG. 2 schematically shows an embodiment of the magnetizing fixture 120according to the present invention. The fixture includes an electricallyconductive structure 210 surrounding an electrically conductive,non-permanently magnetizeable core 220 of substantial magneticpermeability. The electrically conductive structure 210 has anelectrically conductive top 212 attached to second ends of a pluralityof electrically conductive elements or legs 213-218 (213, 217, and 218are shown in FIG. 4) extending therefrom. First ends, i.e., endsopposite from the top 212, (e.g., 219) of the electrically conductiveelements 213-218 alternately couple to either a first electricalconnection 230 or a second electrical connection 240. Thus, if apositive voltage source is coupled to the first electrical connection230 and a negative voltage source is coupled to the second electricalconnection 240, current flows away from the first electrical connection230, through electrically conductive elements 214, 216, and 218, andthrough electrically conductive top 210 before returning to the secondelectrical connection 240 (through electrically conductive elements 215,217, and 213.)

To further illustrate the magnetizing fixture 120, FIGS. 3A-3Dschematically show top, front, side, and cross-sectional views of themagnetizing fixture 120, which also includes an electrically insulatingblock spacer 250 that may be comprised of BAKELITE (phenol formaldehydeor phenolic) and electrically separates electrical connections 230 and240.

The core 220 alters the configuration of magnetic fields generated byelectrical currents flowing through the electrically conductivestructure 210. In particular, because the core 220 has substantialmagnetic permeability, the core 220 alters the magnetic fields inregions external to the core 220 in which the object 130 is immersed toestablish desired magnetization in the object 130. Establishment ofproper magnetization requires confinement of electrical currents to theelectrically conductive structure 210. Without confinement of theelectrical current, the object 130 is exposed to magnetic fields ofimproper strength and variation.

However, efficient production of magnetic fields by electrical currentsrequires close proximity of the core 220 and the electrically conductivestructure 210. In fact, since effective magnetization often requiresminimal space between the magnetizing fixture 120 and the object 130,the electrically conductive structure 210 must often be embedded in thecore 220. Should the core 220 be comprised of an electrically conductivematerial, such as steel, contact between the core 220 and theelectrically conductive structure 210 causes electrical current to leakfrom the electrically conductive structure 210 and distort themagnetization of the object 130. To overcome this problem, aspects ofthe invention confine electrical currents within the magnetizing fixture120 to the electrically conductive structure 210 so as to produce amagnet with desired magnetization. Specifically, aspects of theinvention provide an insulator 640 (see FIG. 6) between the conductivestructure 210 and the core 220.

FIG. 4A-4C schematically shows an embodiment of the conductive structure210, which may be comprised of copper. The electrically conductiveelements 213-218 may have a rectangular cross-section and beperpendicular to the electrically conductive top 212, integrallycoupling to the electrically conductive top 212 via second ends (e.g.,211). The electrically conductive elements 213-218 may be distributed atequal angular intervals about a circumference of the electricallyconductive top 212. Of course, discussion of six electrically conductiveelements 213-218 is exemplary and thus not intended to limit the scopeof the invention.

FIG. 5A-5E schematically show embodiments of the first and secondelectrical connections or bars 230 and 240, which may be comprised ofcopper. The second electrical connection 240 contains a source connector510 and a suspended connector 522. The source connector 510 may containa receptacle 512 to receive the electrically conductive element 217 anda receptacle 514 to receive the electrically conductive element 215. Thesuspended connector 520 may contain a receptacle 522 to receive theelectrically conductive element 213. Likewise, the first electricalconnection 230 contains a source connector 560 with receptacles 562 and564 that may receive the electrically conductive elements 218 and 214and a suspended connector 570 with a receptacle 572 that may receive theelectrically conductive element 216.

FIG. 6 schematically illustrates the electrically conductive core 220,which may be comprised of steel. The electrically conductive core 220contains a top surface 620, a bottom surface 630, and channels 613-618in a side surface 655 coated with an electrically insulating layer 640.The channels 613-618 are open at the top surface 620, at the bottomsurface 630, and along the side surface 655. In some embodiments, theinsulating layer 640 comprises an outer or second sublayer 642 and aninner or first sublayer 644. The outer sublayer 642 may containstabilized zirconia. The inner sublayer 644 may contain a combination ofnickel, chromium, aluminum, and yttrium.

Process 700 for making the magnetizing fixture 120 is summarized in FIG.7. In Step 710, the electrically conductive core 220, the electricallyconductive structure 210, the electrical connections 230 and 240, andelectrically insulating block spacer 250 may be made, for example, bymachining or molding the core 220 from steel, the conductive structure210 and electrical connections 230 and 240 from copper, and the blockspacer 250 from BAKELITE (or another electrically insulating material).

In Step 720, the core 220 is selectively masked to cover the outersurface 650 and to leave uncovered the top surface 620, the bottomsurface 630, and the channels 613-618. Masking may be accomplished bycoating the core with photoresist, exposing the top surface 620, thebottom surface 630, and the channels 613-618 to ultraviolet radiation tocure the photoresist in those areas and dissolving away unexposedphotoresist.

In Step 730, the core 220 is coated with the inner sublayer 644, byspraying and baking a coating containing a combination of nickel,chromium, aluminum, and yttrium, and in Step 740 with the outer sublayer642, possibly stabilized zirconia. In Step 750, the outer surface 650 isunmasked, e.g., by dissolving away the exposed photoresist.

In Step 750, the electrically conductive structure 210 couples to thecoated core 220. For a conductive structure 210 with elements 213-218extending from a conductive top 212 and a coated core 220 with channelsoriented parallel to the side 655 of the coated core 220, the conductivetop 212 may set on top surface 620 of the coated core 220 and theelements 213-218 may lie flush with or be laterally confined, i.e.,lying entirely beneath the outer surface 650 of the coated core 220. Asa result, adjacent electrically conductive elements, e.g. 217 and 218,are connected to receptacles of different electrical connections.

In Step 760, receptacles 512, 514, and 522 of the second electricalconnection 240 receive electrically conductive elements 217, 215, and213. In Step 770, receptacles 562, 564, and 572 of the first electricalconnection 230 receive the electrically conductive elements 218, 214,and 216.

In Step 780, electrically conductive elements 217, 215, and 213 aresilver soldered at a temperature above the melting point of silversolder and below the melting points of copper, steel, zirconia, and acombination of nickel, chromium, aluminum, and yttrium to receptacles512, 514, and 522 and, in Step 790, electrically conductive elements218, 214, and 216 are similarly silver soldered to receptacles 562, 564,and 572 at the electrically conductive element-receptacle joints (e.g.205).

To solder, the temperature of the magnetizing fixture 120 is raised toabout 800° C. and a small torch is used to locally heat the electricallyconductive element-receptacle joints to a temperature above about 940°C. and less than about 1085° C. Since copper melts at about 1085° C.,steel at about 1370° C., zirconia at about 2700° C., and Ni—Cr—Al—Y atabout 1138° C., and silver solder at about 940° C., soldering does notaffect either the core 220, the conductive structure 210, the innersublayer 644, or the outer sublayer 642.

In Step 790, the block spacer 250 is mounted to separate electricalconnections 230 and 240.

The described embodiments of the invention are intended to be merelyexemplary and numerous variations and modifications will be apparent tothose skilled in the art. All such variations and modifications areintended to be within the scope of the present invention as defined inthe appended claims.

1. A method of constructing a magnetizing fixture, the methodcomprising: providing an electrically conductive structure that forms aninterior; providing an electrically conductive core of substantialmagnetic permeability; coating at least a portion of the electricallyconductive core with an electrically insulating material to form aninsulated core; after coating the at least a portion of the electricallyconductive core to form the insulated core, assembling at least aportion of the magnetizing fixture by positioning the insulated corewithin the interior of the conductive structure; and wherein theinsulated core is secured by soldering the conductive structure toanother structure, the soldering being completed at a solderingtemperature, the electrically insulating material having a meltingtemperature that is greater than the soldering temperature.
 2. A methodof constructing a magnetizing fixture, the method comprising: providingan electrically conductive structure that forms an interior; providingan electrically conductive core of substantial magnetic permeability;coating at least a portion of the electrically conductive core with anelectrically insulating material to form an insulated core; aftercoating the at least a portion of the electrically conductive core toform the insulated core, assembling at least a portion of themagnetizing fixture by positioning the insulated core within theinterior of the conductive structure; and wherein coating includesapplying a first layer comprising nickel, chromium, aluminum, andyttrium, and a second layer of stabilized zirconia.
 3. A method ofconstructing a magnetizing fixture, the method comprising: providing anelectrically conductive structure that forms an interior; providing anelectrically conductive core of substantial magnetic permeability;coating at least a portion of the electrically conductive core with anelectrically insulating material to form an insulated core; aftercoating the at least a portion of the electrically conductive core toform the insulated core, assembling at least a portion of themagnetizing fixture by positioning the insulated core within theinterior of the conductive structure; wherein the coating includesapplying a first and a second insulating sublayer; and wherein the firstinsulating sublayer includes at least one of nickel, chromium, aluminum,and yttrium and the second sublayer includes stabilized zirconia.
 4. Amethod of constructing a magnetizing fixture, the method comprising:providing an electrically conductive structure that forms an interior;providing an electrically conductive core of substantial magneticpermeability; coating at least a portion of the electrically conductivecore with an electrically insulating material to form an insulated core;after coating the at least a portion of the electrically conductive coreto form the insulated core, assembling at least a portion of themagnetizing fixture by positioning the insulated core within theinterior of the conductive structure; wherein the coating includes usinga mask; and wherein the coating includes a photoresist.
 5. A method formagnetizing an object, the method comprising: providing a magnetizingfixture connected to an electrical power supply having a first and asecond electrical connection, the magnetizing fixture comprising: (a) afirst electrical connection to the power supply; (b) a second electricalconnection to the power supply; (c) an electrically conductive structurecomprising a plurality of electrically conductive elements and anelectrically conductive top, each element having a first end coupled toone of the first and second electrical connections, each element havinga second end coupled to the electrically conductive top; and (d) anelectrically conductive core of substantial magnetic permeability havinga top surface coupled to the electrically conductive top, a bottomsurface, and plurality of channels communicating from the top surface tothe bottom surface, wherein the top and bottom surfaces and the channelsare coated with an electrically insulating layer and wherein eachelectrically conductive element is contained within a channel;positioning a magnetizable object near the fixture; and using thefixture and power supply to generate a magnetic field so as to magnetizethe object.
 6. A method according to claim 5, wherein the magnetizedobject is a stator.